The present invention relates to a packaging bag provided with a reinforcing member and a method for manufacturing the packaging bag.
For the purpose of preventing the collapse of a packaging bag and improving the self-standing feature, there is conventionally known, for example, reinforcement in which a reinforcing member is used to reinforce a bag body made by bonding together a pair of resin sheets. For example, Japanese Laid-Open Patent Publication No. 2003-191964 discloses a packaging bag in which a thermoplastic resin reinforcing member extends over the upper outer edge and both side outer edges of a bag body.
The reinforcing member described in the above publication is formed as follows. First, as shown in FIG. 6A, the bag body 63 is placed between a lower mold 61 and an upper mold 62, and the molds 61, 62 are clamped. In this states, the upper outer edge and both side outer edges of the bag body 63 are respectively projected only by a predetermined length of L into a recess 61a formed in the lower mold 61. With this state kept, thermoplastic resin is injected to the recess 61a of the lower mold 61, thereby forming a lower divided half 64 of the reinforcing member. Then, as shown in FIG. 6B, the upper mold 62 is allowed to slide in such a manner that the recess 61a of the lower mold 61 is placed opposing a recess 62a formed in the upper mold 62. With this state kept, thermoplastic resin is injected to the recess 62a of the upper mold 62, thereby forming an upper divided half 65 of the reinforcing member. The reinforcing member is constituted with the thus formed lower divided half 64 and upper divided half 65.
When the packaging bag falls, for example, and such an impact that allows mutually-bonded resin sheets of the bag body 63 to be spaced away from each other is given to the packaging bag, the reinforcing member may be broken or peeled off the bag body 63, depending on the magnitude of the impact. Therefore, in view of preventing the reinforcing member from being broken or peeled off, it is preferable to project the upper outer edge and both side outer edges of the bag body 63 greatly into the recesses 61a, 62a of the molds 61, 62 on injection molding of the reinforcing member, thereby forming the reinforcing member having a greater width. As the reinforcing member is made greater in width, the reinforcing member is increased in impact resistance, thereby preventing the reinforcing member from breakage or peeling.
However, when the upper outer edge or the side outer edge of the bag body 63 is greatly projected into the recesses 61a, 62a of the molds 61, 62, as shown in FIG. 6C, the upper outer edge or the side outer edge of the bag body 63 tends to sag or warp inside the recesses 61a, 62a. In particular, on injection of thermoplastic resin into the recesses 61a, 62a, there is a case where the upper outer edge or the side outer edge of the bag body 63 may warp by heat and flow of injected thermoplastic resin. When the upper outer edge or the side outer edge of the bag body 63 sags or warps inside the recesses 61a, 62a of the molds 61, 62, a difference in thickness occurs between a part of the reinforcing member positioned on the surface of the upper outer edge or the side outer edge of the bag body 63 and a part of the reinforcing member positioned on the back face thereof. As a result, impact resistance of the reinforcing member cannot be sufficiently improved. Further, when the upper outer edge or the side outer edge of the bag body 63 is at least partially exposed outside the reinforcing member because of the sag or warp of the upper outer edge or the side outer edge of the bag body 63, the appearance of the packaging bag will be degraded.